Feedback control method for the operation of a centrifuge

ABSTRACT

A feedback control method accounts for noise emissions of a centrifuge for the operation of a centrifuge, in particular a separator or a decanting centrifuge, for the centrifugal processing of a product, in particular for clarifying a product and/or for separating a product into different liquid phases using the drum.

BACKGROUND AND SUMMARY OF THE INVENTION

Exemplary embodiments of the invention relate to a method forcontrolling the operation of a centrifuge with a rotatable drum, inparticular a separator or a decanter, in the centrifugal processing of aproduct, in particular in a clarifying of a product and/or in aseparating of a product into different liquid phases with the drum.

Such methods are known per se from the prior art, thus from Germanpatent document DE 100 24 412 Al or PCT International patent document WO97/20634. German patent document DE 40 04 584 A1 discloses evaluatingnoise development of the centrifuge in the controlling of the separationprocess for optimization of the separation process.

With respect to this prior art, a further method is to be created forthe operation of a centrifuge, which enables optimized modes ofoperation compared to the prior art.

According to an exemplary embodiment, in the controlling of theoperation of the centrifuge the noise development of the centrifuge iscontrolled, by

-   -   a. at least one noise level limit being defined,    -   b. during operation, i.e., during a rotating of the drum of the        centrifuge, the noise development of the centrifuge being        measured by a sensor device,    -   c. the data measured by the sensor device being passed on to a        control device, by which the measured data are compared to        target data, and by which, using this comparison, at least one        correcting variable is determined, and    -   d. with the control device, using the at least one correcting        variable or using a plurality of correcting variables, the        operation of the centrifuge is influenced so that the noise        development does not exceed the at least one noise level limit.

In such a way, the ongoing operation of the centrifuge is optimized inthe centrifugal processing of a product, wherein the focus is not oronly marginally an error detection, but rather a minimizing of the noisedevelopment as a function of at least one or more predetermined limits.

An optimization of the noise development as a function of predeterminednoise development limits means, in particular, the reduction of thenoise emission or respectively the reduction of the loudness of thecentrifuge as a function of predetermined limits. Here, by way ofexample, the sound pressure level is named as a measurement. The soundpressure is measured here in μPa and is set in relation to a referencesound pressure level p₀=20 μPa=2×10⁻⁵ Pa, so that it can be indicated indB (decibels). Further conceivable physical values as a basis for thereduction of the sound intensity of the centrifuge are, however, alsothe sound power level (indicated in dB), the loudness (indicated in“sone”), the sound intensity in phon, or evaluated sound pressure—orrespectively sound power level. The A-weighted sound level is basedhere, for example, in a frequency-dependent manner on human hearing withcorrection factors, in order to be able to better replicate theperceived sound intensity. The calculation of the total sound pressurelevel then takes place.

The sound pressure level L_(p) is calculated here according to thefollowing formula:

L_(p)=20 log₁₀ (p/p₀) dB, wherein p stands for the measured pressure andp₀ stands for the reference sound pressure level.

Example: Correction factors k for an A-weighted sound measurement:

Frequency [Hz] 100 200 400 1000 2000 4000 8000 12000 Correction −19.1−10.9 −4.8 0 +1.2 +1.0 −1.1 −4.2 factor k [dB]

The sum sound pressure level is calculated here according to thefollowing formula:

L=10×log ₁₀ ((p ₁ ² +P ₂ ² + . . . +p _(n) ²):(p ₀ ²))

The invention is described in further detail below with reference to thedrawings by means of an example embodiment.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows a diagrammatic illustration of a separator for thecentrifugal processing of a product,

FIG. 2a and b show two views of a further separator for the centrifugalprocessing of a product; and

FIG. 3a and b show two views of a decanter for the centrifugalprocessing of a product.

FIG. 4a and b show two diagrams, which illustrate a noise reduction bymeans of variants of methods according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a diagrammatic illustration of a separator for thecentrifugal processing of a product, in particular for clarifying aproduct of solids (or for concentrating such a phase) and/or forseparating a product into different liquid phases.

The separator illustrated in FIG. 1 has a rotatable drum 1 (onlyillustrated schematically here), with a preferably vertical rotationaxis, which has a drive spindle (not illustrated here), which can bedriven via a drive connection (likewise not illustrated here) with amotor 2. A supply line 3 leads into the drum 1. Liquids of differentdensity and, if applicable, solids, can be directed out from the drumthrough one or more discharge lines 4, 5 and, if applicable, solidsdischarge openings 6. In the supply line 3 and the discharge line(s) 4and 5, valves are provided (not illustrated here), which are preferablycontrollable (and preferably able to be throttled).

The rotatable drum 1 and preferably the drive/motor 2 are arranged on amachine frame 13. The machine frame 13 is, in turn, mounted on a base 15via one or more foot elements 14, which may have a spring or can beconstructed as such. In FIG. 2, this spring is illustrated as a block16.

During operation, i.e., during rotation of the drum 1, the noisedevelopment of the centrifuge, in particular in the vicinity of the drum1, is measured with a suitable sensor device, in particular with amicrophone 7. This measuring takes place in ongoing manner continuously,or at intervals. The data measured by the sensor device are passed on toa control device 8 (which has, inter alia, a computer), where they areevaluated. Thus, respectively, only the sound level can be measured.However, it is also conceivable to receive and evaluate a frequencyspectrum. In FIG. 2 a microphone 7 is also illustrated and alternativelya sensor 7′ for measurement directly on a cover of a separator.

The measurement data are then compared with target data. At least onecorrecting variable is determined using this comparison. The controldevice 8 uses the at least one correcting variable (or severalcorrecting variables) to influence the operation of the centrifuge sothat the control variable—the noise development—is altered so that itassumes a desired behavior.

Thus, it is conceivable to feed to the motor or respectively itscontrol, for example to a frequency converter 2, via a line 9 (orwirelessly), a signal influencing the rotation speed of the drivespindle of the drum 1, in order to alter the rotation speed of the drivespindle, in order to alter in such a way the noise development of theseparator, in particular to reduce it.

It is also conceivable to include further parameters into the control.Thus, in addition to the rotation speed, factors influencing noisedevelopment are the feed 3 and/or the outlet pressures into the outlets4, 5 and/or the emptying amount/emptying frequency via the outlet 6 ofthe drum 1. Thus, the noise development on emptying operations, e.g., bymeans of a piston slide valve at discharge openings—with a smallervolume is less than in emptying operations of solids with a greatervolume.

For this, however, emptying operations are necessary more frequently, inorder to achieve overall the intended emptying volume.

For this, it is advantageous to actuate devices, in particular valves,which are able to be actuated via data lines (or wirelessly) 10, 11, 12,in the discharge lines 4, 5, 6 such that the throughflow behavior in thecorresponding supply and discharge lines is altered so that the noisebehavior (within a predetermined noise level window) is optimized asdesired.

Particularly preferably, the airborne sound transmitted by thecentrifuge and surrounding machine parts and/or by a gas surrounding thedrum is determined by the sensor device. Alternatively, thestructure-borne sound could also be detected. The preferably detectedfrequency band both for the airborne sound measurement and also for thestructure-borne sound measurement is 50-12000 Hz, preferably 50-8000 Hz,most particularly preferably 50-5000 Hz.

Thus, it is in fact known from the prior art, for example to sense thevibration behavior of centrifuges using deflections of the drivespindle. On the other hand, it was not recognized that the noisedevelopment presents a simple possibility for controlling the operationof the centrifuge, which offers other and/or further advantages comparedto the prior art.

For example, it is conceivable to define one or more upper noise levellimits I and II, and to operate or respectively control the machine sothat depending on the time of day, one or other of the limits is adheredto, for example in order to adhere to noise regulations which stipulatea quieter operation at night than during the day.

Preferably, the outlet pressures, the volume flow that is to beprocessed, the emptying amount, the emptying frequency, and the rotationspeed of the drum are controlled as correcting variables. If, forexample, a separator MSE 500 at 50 m³/h and 6 bar outlet pressuregenerates a sound pressure of 84 dB(A) (measured by way of example at 1m distance), this delivers during operation with 35 m³/h and 4.5 baroutlet pressure a distinctly reduced sound pressure of only 80 dB(A).The control of the noise level is preferably supplemented by a controlof further variables, for example control of the turbidity using aturbidity measurement in the outlet for determining the degree ofseparation.

It is preferred that the noise level measurement takes place inintervals which are less than or equal to 1 h, preferably less than orequal to 10 min, in particular less than or equal to 1 min. However, itis also conceivable to carry out the measurement more infrequently, forexample only when a change to the noise level is desired after apredetermined time of day.

The method according to the invention is suitable for the operating of acentrifuge, in particular a separator with vertical rotation axis incontinuous operation, which has a separation means such as a separationdisk set in the drum. Alternatively, the centrifuge can be constructedin a different manner, for example as a solid bowl screw-typecentrifuge, in particular with a horizontal rotation axis (notillustrated here).

By suitable selection of the distance of the sensor device to thecentrifuge, an influence can be carried out as to whether more or fewernoise influences from the environment also enter into the measurement.The conventional distance to the surface of 1 m is, for example, set atless than 1 m here, in particular less than 50 cm, particularlypreferably at less than 30 cm.

It is also conceivable to detect the environmental noises and the noisesof the centrifuge with two sensor devices such as microphones, which arepreferably directed in different directions, in particular offsetthrough 180°, and to use these for evaluation. Thus, the difference ofthe noise development between the environment and the centrifuge couldbe determined, because in the environment generally there are furthermachines such as mills or pumps, which influence the noise development.It is also conceivable to also include environmental machines into thenoise-dependent regulation/control.

When structure-borne sound is measured, this measurement, preferablysensing on the oscillating system of the centrifuge will take place at alocation that can oscillate particularly intensively, for example on thecover. The machine itself must be insulated from the environment via oneor more dampers. In such a way, the influence of the structure-bornesound from the environment on the measurement of the noise developmentcan be minimized. FIGS. 2 and 3 illustrate this by the example of aseparator (FIG. 2) with vertical rotation axis with a structure-bornesound sensor 7′ (or respectively-receiver, in particular anelectroacoustic transducer for structure-borne sound measurement) formeasurement of the structure-borne sound on the oscillating system, hereon a cover 17 surrounding the drum, which is particularly well suitedfor this. Other locations on the separator with vertical rotation axisor on a decanter (solid bowl screw-type centrifuge) 18 with horizontalrotation axis 19.

According to the variant, illustrated in FIG. 4a , of a method accordingto the invention, a noise level threshold value I is to be adhered to orrespectively as far as possible not or if only briefly exceeded. First,a noise level threshold value I is set. In operation, thestructure-borne sound and/or the air-borne sound is determined formeasuring the noise development of the centrifuge, and namely herepreferably using a microphone or several microphones 7 as sensor device.As can be seen in FIG. 4a , the noise level threshold value I on runningup to a nominal rotation speed (operating instants 1. to 2.) and then inidling (ready for operation, operating instants 2. to 3.) at nominalrotation speed is not yet reached or respectively is fallen below. Thenin operation with the centrifugal processing of the product (operatinginstants 3.-4.) the noise level threshold value is reached and thenexceeded. This is determined with the control device, which alsocalculates an altered correcting variable—here an altered rotationspeed. Then (operating instants 4.-5.) the control device 8 reduces therotation speed (see also FIG. 1) down to the renewed falling below ofthe noise level threshold value I. This method can be readily appliede.g. in separators, in particular nozzle separators, or decanters.

According to the variant of a method according to the inventionillustrated in FIG. 4 b, again a noise level threshold value I is to beadhered to or respectively as far as possible not or if only brieflyexceeded, which, however, in contrast to in FIG. 4a is defined not as apeak value but rather as a mean value of the noise development. First,the thus defined noise level threshold value/mean value I is set. Inoperation, the structure-borne sound and/or the air-borne sound isdetermined for measuring the noise development of the centrifuge, andnamely again preferably using a microphone or several microphones 7 assensor device. FIG. 4b shows the noise development at so-calledself-emptying separators, in which solids are emptied at intervals by abrief opening of solids discharge openings. With few large emptyingoperations (instants 1′ and 2′) a higher mean value occurs for the noisedevelopment than with several small emptying operations (instants 3′ and4′). In such a way, when the mean value is exceeded, the emptying amountat the outlet and the emptying frequency at the outlet 6 of the drum 1of the separator is advantageously and simply used and if applicablealtered by the control device as correcting variables.

Although the present invention has been described above by means ofembodiments with reference to the enclosed drawings, it is understoodthat various changes and developments can be implemented without leavingthe scope of the present invention, as it is defined in the enclosedclaims.

REFERENCE NUMBERS

drum 1motor 2supply line 3discharge lines 4,5solids discharge openings 6microphone 7control device 8line 9data lines 10, 11, 12machine frame 13foot elements 14base 15spring 16cover 17decanter 18rotation axis 19 Page 4

1-15. (canceled)
 16. A method for controlling operation of centrifugewith a rotatable drum while clarifying of a product or in a separatingof a product into different liquid phases with the drum, the methodcomprising controlling noise of the centrifuge by: a. defining at leastone noise level limit; b. measuring, using a sensor while rotating thedrum, noise of the centrifuge; c. providing data measured by the sensorto a controller, wherein the controller compares the measured data totarget data and at least one correcting variable based on thecomparison; and d. controlling, by the controller using the at least onecorrecting variable or a plurality of correcting variables, theoperation of the centrifuge so that the noise of the centrifuge does notexceed the at least one noise level limit.
 17. The method of claim 16,wherein the measured noise is structure-borne sound or air-borne sound.18. The method of claim 16, wherein the sensor is one or moremicrophones.
 19. The method of claim 16, wherein sensor is at least onepiezo sensor or at least one laser Doppler vibrometer.
 20. The method ofclaim 16, wherein the sensor continuously measures the noise of thecentrifuge.
 21. The method of claim 16, wherein the sensor measure thenoise of the centrifuge at intervals.
 22. The method of claim 17,wherein the intervals are less than or equal to 1 minute.
 23. The methodof claim 16, wherein the at least one correcting variable is rotationspeed of a drive spindle of the rotatable drum.
 24. The method of claim16, wherein the at least one correcting variable is outlet pressure orpressures in an inlet or in one or more outlets of the rotatable drum.25. The method of claim 16, wherein the at least one correcting variableis processed volume flow.
 26. The method of claim 16, wherein the atleast one correcting variable is an emptying amount at an outlet of thecentrifuge.
 27. The method of claim 16, wherein the at least onecorrecting variable is an emptying frequency at an outlet of thecentrifuge.
 28. The method of claim 16, wherein the at least one noiselevel limit includes at least a first and second upper noise level limitand one of the first and second upper noise level limits is selected forcontrolling the centrifuge based on time of day.
 29. The method of claim16, wherein the control of the noise is combined with a turbity control.30. The method of claim 16, wherein the sensor measures structure-bornesounds on a cover of the centrifuge.